1. Field of the Invention
The present invention relates to a method for forming fin structures for non-planar semiconductor device, and more particularly, to a method for forming fin structures for non-planar semiconductor device using sidewall image transfer (hereinafter abbreviated as SIT) technique.
2. Description of the Prior Art
Conventional planar metal-oxide-semiconductor (MOS) transistor has difficulty when scaling down to 65 nm and below. Therefore the non-planar transistor technology such as Fin Field effect transistor (FinFET) technology that allows smaller size and higher performance is developed to replace the planar MOS transistor.
The FinFET device is conventionally formed by: First a silicon layer of a substrate is patterned to form fin structures (not shown) by a proper etching process. Then, an insulating layer surrounding lower portions of the fin structures is formed and followed by forming a gate covering a portion of the insulating layer and top portions of the fin structures. Immediately next, dopants are introduced and annealing treatments are performed to form source/drain in the fin structures not covered by the gate. Since the manufacturing processes of the FinFET device are similar to the traditional logic device processes, it provides superior process compatibility. More important, since the FinFET device increases the overlapping area between the gate and the fin structures, the channel region is more effectively controlled. This therefore reduces drain-induced barrier lowering (DIBL) effect and short channel effect, and the current between the source and the drain is increased.
However, the FinFET device still faces many problems. It is found that fin widths of fin structures in different regions are made different after fabrication processing, though it is supposed to be identical. For example, fin width is reduced due to silicon loss in thermal treatment, and such problem is exacerbated in iso region(s). It is well-known that the fin width is a key factor for device performance, therefore fin width control is important. Accordingly, method for manufacturing fin structures with consistent fin widths is still in need.